DEVELOPMENT OF A NEW THERMO-MECHANICAL ENVIRONMENTAL FATIGUE TESTING FACILITY TO INVESTIGATE THE IMPACT OF THERMAL STRAIN GRADIENTS ON FATIGUE INITIATION

摘要

Light water reactor coolant environments are known to significantly reduce the fatigue life of austenitic stainless steels. However, most available data are derived from isothermal testing of membrane loaded tensile specimens, whereas the majority of plant loading transients result from thermal transients and involve significant through-wall strain gradients. This paper describes the development of a high temperature water facility to enable both thin and thick wall hollow fatigue endurance specimens to be subjected to thermal and mechanical loading for a wide range of thermal cycles including rapid shock loading. Thermal shock loading from 300°C to between 40 and 150°C has been achieved and Finite Element Analysis, FEA, has been used to calculate the thermally induced strain profiles through a 12mm thick-wall specimen. This indicates peak surface thermal strain ranges of up to 0.8% for a transient between 300 and 40°C. Testing is underway to investigate the impact of the strain gradient and thermal waveform on the fatigue life of this specimen where significantly longer lives may be expected compared to membrane loaded specimens. The ability within the same facility to apply simulated thermal shock profiles to both thick-wall specimens and mechanically loaded thin wall specimens provides a powerful tool to assess the impact of thermal fatigue loading and thermal strain gradients on component life.